1. Field of the Invention
The present invention relates to a propylene polymer (PP) resin composition. More particularly, it relates to a propylene polymer (PP) resin composition which can be advantageously used as a molding material for producing PP molded parts required to have a well-balanced combination of rigidity and impact resistance. Examples of such PP molded parts include automotive internal and external trim parts required to have impact resistance as well as rigidity, such as lamp housings, trims, console boxes, grilles, pillar garnishes, etc.
2. Background Information
For producing automotive internal and external trim parts such as those mentioned above, PP resin compositions are recently being used in large quantities as molding materials, from the standpoints of material cost and light weight.
Since those molded parts are required to have both rigidity and impact resistance, PP resin compositions having impact-resistance have normally been used in which the polymer ingredients consist mainly of blends of a propylene-ethylene block copolymer (B-PP) and an ethylene- propylene rubber (EPR). (See, for example, JP-A-53-64257; the term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, the resin composition whose polymer ingredient consists mainly of the above-described polymer blend has had the following problems. In the case where molded parts having a certain degree of impact resistance (for example, 15 kgf.cm/cm (147 J/m) or more) are to be obtained, it is necessary to use a B-PP having a relatively high molecular weight (a relatively low MFR), so that the resulting composition is caused to have processability problems. (Normally, an MFR of 8 g/10 min. or more is required.) This poor processability is apt to adversely affect the finish of the final molded products. In addition, sufficient rigidity (for example, 22,000 kg/cm.sup.2 (2160 MPa) or more in the case of formulations containing 25% of talc) has been difficult to obtain (see Comparative Example 1 in Table 4 below).
In the following description, the amounts of ingredients blended or incorporated are given by weight unless otherwise indicated.
Following is a list of abbreviations used herein.
PP . . . propylene polymer PA0 B-PP . . . crystalline propylene polymer of an ethylene-propylene block copolymer type PA0 EPR . . . ethylene-propylene rubber PA0 PE . . . polyethylene PA0 HDPE . . . high-density polyethylene PA0 LDPE . . . low-density polyethylene PA0 MFR . . . melt flow rate (the amount of polymer that is extruded from a nozzle having a diameter of 2.095 mm and a length of 8 mm at a temperature of 230.degree. C. within 10 minutes under a load of 2.16 kgf (21.2 N); refer to ASTM-D1238.) PA0 ML.sub.1+4 (100.degree. C.) . . . Mooney viscosity (measured using the large disc (L) after one-minute warm-up at 100.degree. C. and four-minute disc rotation)